“The great tragedy of Science,” observed biologist Thomas Huxley in 1870, is “the slaying of a beautiful hypothesis by an ugly fact.” Yet some ideas, once rooted, believed, and publicized, become hard to kill. They become what economist John Quiggin called zombie ideas—ideas that survive repeated refutations and return to feed on people’s brains.
In earlier posts, I offered my 10-item list of psychology’s mind-munching, refuse-to-die ideas. And I offered seasonal affective disorder (with its apt acronym, SAD) as one candidate example. SAD—popularly thought of as winter blues—is a widely acknowledged psychiatric diagnosis, with a prominent place in the Diagnostic and Statistical Manual of Mental Disorders (as depressive disorder “with seasonal pattern”), on the National Institute of Mental Health website, and in the public health information provided by the esteemed Mayo Clinic, Cleveland Clinic, and Johns Hopkins, not to mention (ahem) prominent psychology textbooks.
The DSM, which defines “seasonal pattern” as a person’s recurring depression in any particular season, doesn’t wed SAD to wintertime. But most folks understand SAD as does NIMH: “In most cases, SAD symptoms start in the late fall or early winter and go away during the spring and summer, known as winter-pattern SAD or winter depression.” Surely these esteemed sources are right to presume that many people suffer prolonged sadness, withdrawal, and irritability during the dreary, sun-deprived weeks around the winter solstice?
I took my profession’s word for it. But then I encountered some ugly facts, which caused me to dig deeper.
Seasonality, Sun, and Sadness
The first big challenge to my belief in SAD—my assumption that depression risk increases with decreasing daylight—came from 34,294 respondents to a 2016 Centers for Disease Control and Prevention annual health study. Auburn University at Montgomery researchers Megan Traffanstedt, Sheila Mehta, and Steven LoBello noted people’s self-reported mental health, then asked:
- Is depression more common in the days surrounding the December winter solstice?
- Is wintertime depression greater for those living in daylight-deprived northern latitudes?
- Is it greater for those living in mostly cloudy rather than sunny communities?
- Is it greater for those not experiencing sunny skies on the interview day?
Their stunning, consistent answers: No. No. No. And no.
Moreover, they reported, other research confirms that SAD, though “strongly rooted in folk psychology . . . is not supported by objective data.” The long winter darkness of northern Norway, for example, is unaccompanied by increased depression.
Seasonality and Information Searches
So, is SAD like the oft-reported but elusive Loch Ness Monster? As impressive as these data were I hesitated to slay the “beautiful hypothesis” that SAD is real. It has been many people’s self-reported experience. It is affirmed by many mental health and medical professionals. And light therapy’s effectiveness seemingly confirms that light deprivation matters. (Check that: A new review reveals that that bright light therapy actually helps relieve nonseasonal depression as well.)
So, as a further test, I wondered if Google searches across a year’s time would confirm or disconfirm people experiencing wintertime depression. First, to illustrate and validate the method, I instructed Google Trends to display Americans’ searches for two clearly seasonal experiences: “basketball” and “flu.”
As we would expect, both showed wintertime surges, with “basketball” peaking during the NCAA’s March madness tournament time. Ditto the expected surge in “prostate” searches after news of President Biden’s prostate cancer:
So, is there a corresponding wintertime surge in people seeking information about sadness and depression? There is not. Ditto for Canadian and British Google searches. And ditto for searches of other mood-related words such as “depression” and “suicide.”
Seasonality and Suicides
So, people’s self-reported depression and their internet searches do not display seasonal affect variation. But what about their behavior? Are suicides more frequent in wintertime? Do suicides spike during the supposed Christmas “holiday blues”?
The CDC provides a clear answer: They do not.
Data from other countries confirm that, if anything, there is a wintertime dip in suicides, with a slightly higher suicide rate in the sunniest months—now here in the northern hemisphere, but November into March in Australia and Brazil.
Sometimes science surprises us. I once believed in seasonal affective disorder. Am I wrong, in the face of these data, now to disbelieve—and to see occasional human misery as a year-round malady? Even some SAD believers approach the same conclusion, by claiming that SAD strikes some people in the summer, or in the fall. Why not, looking at the data above, add the spring, too—year-round SAD! But isn’t a SAD for any season a SAD with no season?
To quote my favorite detective, Agatha Christie’s Miss Marple, “Facts are facts, and if one is proved to be wrong, one must just be humble about it and start again.”
David Myers, a Hope College social psychologist, authors psychology textbooks and trade books, including his recent essay collection, How Do We Know Ourselves? Curiosities and Marvels of the Human Mind.
